Process for producing ethylxylene and meta xylene



N. STEIN Aug. 20, 1957 PROCESS FOR PRODUCING ETHYLXYLENE AND META XYLENE Filed Oct. 6, 1955 mS b E Nbrman Stein 1 N V EN TOR.

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msukam N mm R R R. n d mm mm QQ .WQQ QQ R w r @mui l ATI'Ok/VEY United States Patent Norman Stein, Chicago, Ill., assignor to Standard Oil Company, Chicago, 11]., a corporation of Indiana Application October 6, 1955, Serial No. 538,866

3 Claims. (Cl. 260--674) This invention relates to the preparation of very high purity 1,3,5-ethylxylenc and meta-xylene by interaction of ethylbenzene and a xylene in the presence of HFBF3 catalyst. More particularly, the invention relates to the recovery of 1,3,5-ethylxylene and m-xylene in very high purity from HFBF3 complex.

I It is possible, by the use of HF-BF3 treating agent and appropriate conditions of time and temperature, to interact ethylbenzene and at least one xylene isomer to obtain in the acid phase essentially only 1,3,5-ethylxylene as the C aromatic hydrocarbon product and essentially only meta-xylene as the xylene product. This is, these essentially pure isomers are obtainable when the acid phase is decomposed utilizing water or dilute caustic at very low temperature; under these conditions, the HF and BFs are removed from the aromatic hydrocarbon complex and changed into forms which do not catalyze isomerization of the ethylxylene and xylene.

When it is desired to recover the aromatic hydrocarbons from the acid phase by techniques which permit the reuse of the HF and the BFs, it has been found that very high purity 1,3,5-ethy1xylene and meta-xylene cannot be readily obtained. It appears that when the BFs is driven from the complex without simultaneously removing substantially all the HF, some back isomerization of the 1,3,5-ethylxylene to other ethylxylene isomers and meta-xylene to other xylene isomers takes place. It is possible, by the use of high vacuum at relatively low temperatures, to remove HF and BE; overhead with essentially no back isomerization of the desired products, namely 1,3,5-ethylxylene and meta-xylene. It is obvious that high vacuum distillation at relatively low temperatures is not an economic operation.

An object of the invention is a process for preparing very high purity. 1,3,5-ethylxylene and meta-xylene, which process recovers HF and BFs in usable form. Another object is a process for continuously decomposing an HF- acid phase containing dissolved 1,3,5-ethylxylene and meta-xylene as complexes with HF and BFs and recovering very high purity 1,3,5-ethylxylene and meta-xylene and also the HF and BFs in reusable form. Other objects will become apparent in the course of the detailed description.

It has been discovered that a liquid HF-acid phase containing dissolved therein complexes of 1,3,5-ethylxylene as essentially the only ethylxylene and meta-xylene as essentially the only xylene with HF and BF3 can be continuously fractionally distilled to decompose the complex and take HF and BFs overhead and the meta-xylene and 1,3,5-ethylxylene recovered in about the same purity as they existed in the acid phase, by operating the fractional distillation column at a tower top pressure between about and 60 p. s. i. a. and a tower pot temperature at about the bubble point of meta-xylene at the particular pressure.

The invention is described in detail in connection with the annexed figure which forms a part of this specification. It is to be understood that the figure is schematic ICC in nature and represents only one embodiment of the invention; other embodiments may be readily made by those skilled in this art.

In the figure, feed from source 11 is passed by way of line 12, pump 13, and line 14 into reactor 16. The feed consists essentially of ethylbenzene and at least one xylene isomer other than meta-xylene. The xylene isomer may be either ortho-xylene, para-xylene, a mixture of these twoxylenes, or a mixture of one or both these xylenes with metaxylene. The preferred feed is a natural mixture of the xylene isomers and ethylbenzene such as is derived from catalytic reformed petroleum naphthas or from distillation from the light oil derived from coking of coal. While some small amount of non-aromatic hydrocarbons, close boiling about the xylene boiling range are tolerable, it is preferred that the feed be essentially pure aromatic hydrocarbon and contain not more than about 3-5 volume percent of non-aromatic hydrocarbons. As a result of the recent advance in solvent extraction, it is now possible to obtain from petroleum sources mixtures of C8 aromatic hydrocarbons containing, within experimental error, no non-aromatic hydrocarbons.

The process involves an interaction of xylene with ethylbenzene to form ethylxylene and benzene. In order to react essentially all the ethylbenzene and thereby obtain a xylene product containing little or no ethylbenzene, it is necessary to have present a mole ratio of xylene to ethylbenzene of at least 1. More than this amount of xylene is desirable and it is preferred to operate with a mole ratio of between about 3 and 5:1. In this embodiment, the feed is a mixture of C3 aromatic hydrocarbons containing only trace amounts of non-aromatic hydrocarbons, which feed has been derived by solvent extraction from a catalytic retormate. This feed contains about 20 mole percent of ethylbenzene, about 40 mole percent of meta-xylene, and the remainder ortho and paraxylene.

HP from drum 18 is passed by way of line 19, pump 21, and line 22 into line 23. The process is carried out under substantially anhydrous conditions and therefore the HF charged has not more than about 2 or 3 weight percent of water. Commercial grade anhydrous hydrofluoric acid which normally contains only about 1 weight percent of water is particularly suitable for use in the operatio-n. In this embodiment, commercial grade anhydrous hydrofluoric acid is utilized as make-up and is passed from source 24- by way of valved line 26 into HF drum 18.

Recycle BFs from line 31 is passed into line 23. Commercial grade BFs from source 32 is passed by way of valved line 33 into line 31 when make-up is needed. The HP and BFs in line 23 are passed into a lower portion of reactor 16..

In order to obtain the desired products, namely 1,3,5- ethylxylene and meta-xylene in the desired very high purity form, namely about 94-95% or better, it is necessary to adjust the conditions in reactor 16 in a definite fixed manner. It is necessary to have in reactor 16 at least about 1 mole of BFa per mole of xylene in the feed. For example, at 0.9 mole of BF per mole of xylene in the feed, the presence of some uncomplexed xylene results in very marked increase in interaction rate. However, maximum purity meta-xylene is not obtainable by the use of less than 1 mole of BB per mole. More than 1 mole of BF? per mole of xylene in the feed is desirable. It is preferred to operate with between about 1.5 and 3 moles of BF per mole of aromatic hydrocarbon charged.

The reaction is a liquid phase reaction and suflicient pressure is maintained on the reactor to keep the HF in the liquid state. Since an excess of BFz is used over that which will complex with the aromatic hydrocarbons and also dissolve in the liquid, bubbles of BE; and even some BF3 gaseous phase may be present in the reactor. It is preferred to design the reactor so as to have essentially no separate gas phase other than as bubbles dispersed through the liquid. Suflicient liquid HF must be present to participate in the formation of a complex with the polyalkylbenzenes and the BFz. It is believed that one mole of HF is present per mole of polyalkylbenzene present in the reactor in the complexed condition. In addition to the HF going to form the complex, it is necessary to have HF present to dissolve the complex. When suflicient HF is present, a separate distinct acid phase appears. More than this minimum amount of HF is desirable in order to speed up the reaction rate and have a less viscous system. It is preferred to operate with between about 5 and 25 moles of liquid HF per mole of aromatic hydrocarbon charged to reactor 16. In this embodiment, 1.7 moles of BF3 are used per mole of total aromatic hydrocarbon in the feed and 12 moles of HF per mole of total aromatic hydrocarbon in the feed.

Under these conditions of HF and E15 usage, all the aromatic hydrocarbon is dissolved into the HF acid phase and there appears to be in the reactor only one liquid phase. Because of this essentially homogeneous liquid phase, it is not necessary to provide elaborate stirring mechanism within reactor 16. In this embodiment, reactor 16 is operated as a plug-flow reactor with the HFBF3 and feed intermingling at the bottom of the reactor and flowing without substantial turbulence up through the reactor and leaving the reactor at the top by way of line 36.

Competing reactions take place and it is necessary to adjust the time and temperature conditions in reactor 16 to insure the formation essentially only of the desired 1,3,5-ethylxylene and meta-xylene. The temperature in reactor 16 is maintained between about 100 F. and about 300 F. The residence time of the aromatic hydrocarbons in the reactor 16 is dependent upon the temperature within reactor 16. At these temperatures, the residence time may be between about minutes and about 6 hours; the lower the temperature, the longer the time needed to attain the desired purity product so that the longer contacting times correspond to the lower contacting temperatures. It is preferred to operate at a temperature between about 175 F. and about 225 F.; the corresponding times are between about 75 minutes and about 30 minutes. In this embodiment, the temperature in reactor 16 is maintained at 185 F. and the total time of contacting is about 65 minutes.

From reactor 16, the liquid acid phase and BFs are passed by way of line 36 into decomposer 37. Decomposer 37 is a tower adapted for the continuous fractional distillation of liquids. It is provided with a reflux coil 38 positioned near the top of the tower and an internal heat exchanger 39 set in the pot of the tower. Also, the decomposer is provided with vapor-liquid contacting means not shown. These may be either conventional packing or bubble cap type of contacting means. The material from line 36 is introduced in the tower at a point about midway between the top of the pot and the exit conduit from the tower.

In order to produce a bottoms product containing essentially no BF and hardly more than trace amounts of HF, it is necessary to operate the tower at a temperature high enough to drive the HF and BF; overhead. The BFs, both uncomplexed and complexed, is removed from the acid phase fairly readily. The liquid HF, which has a boiling point of 70 F., is removed more slowly. It is believed that the HF acts as a catalyst for the back isomerization of 1,3,5-ethylxylene to a mixture of ethylxylene isomers and meta-xylene to a mixture of xylene isomers. Therefore, it is necessary to remove the HF from the aromatic hydrocarbons sufficiently rapidly to essentially avoid the back isomerization reaction.

Decomposer 37 is operated at a tower top pressure measured at about the point where vapor leaves the top of the tower through conduit 41 between about 20 and 60 p. s. i. a. In order to obtain the rapid removal of HF, decomposer 37 is operated with a pot temperature of essentially the bubble point of meta-xylene at the particular pressure maintained at the tower top. By operating at these conditions, not only is the HF and the BFs removed at a rate such that very little back isomerization occurs, but also the amount of hydrocarbons taken overhead is maintained at a minimum with essentially all of the xylene and all of the ethylxylene product being taken as a liquid bottoms product. (Normally, in reactor 16, some disproportionation of xylene occurs to form mesitylene and toluene. The toluene is taken overhead in decomposer 37 along with the benzene by-product of the interaction. The mesitylene product is taken as a liquid bottoms product. However, by very careful control of the time and temperature conditions in reactor 16, it is possible to substantially eliminate the xylene disproportionation reaction.)

In general, in the process the tower pot temperature, under the defined tower top pressure conditions, will be between about 305 F. and 345 F. The lower temperatures correspond to the lower pressures. In general, when operating with the feed utilized in this embodiment, the tower pot temperature is about 320 F. and the tower top pressure is about 40 p. s. i. a. In this embodiment, decomposer 37 is operated at a tower top pressure of 22 p. s. i. a. and a tower pot temperature of 310 F.

There is taken overhead, by way of line 41, a stream of BFs, HF vapor and benzene vapor. This stream is passed through cooler 42 and the cooled stream is passed by way of line 43 into separator 44. Separator 44 is adapted for removing liquid from a gaseous stream. Liquid product benzene is removed from separator 44 by way of line 46. Liquid HF is removed from separator 44 by way of line 47 and is passed by way of line 48 to HF drum 18.

BFa gas and some HF vapor are removed from separator 44 by way of line 51 and passed through compressor system 52. In compressor system 52, more HF is condensed and is passed by way of lines 53 and 54 to manifold 56; from manifold 56 the liquid HF is passed by way of lines 57 and 48 to drum 18. The recovered BFs, compressed to operational pressure, is passed by way of lines 31 and 23 back to reactor 16.

The aromatic hydrocarbons bottoms product is removed from decomposer 37 by way of line 86 and is passed into fractionation system 87. The liquid bottoms product contains some benzene, a small amount of mesitylene and xylene. Essentially the only Cs aromatic hydrocarbon is meta-xylene. Some small amount of ethylbenzene is present in the C8 fraction as well as unconverted ortho and para-xylene. The benzene-toluene stream is taken overhead by way of line 88. The metaxylene product is shown as being removed as a side stream by Way of line 89. The bottoms product consists essentially of 1,3,5-ethylxylene with very small amounts of other ethylxylene isomers. (Any mesitylene present in this stream may be separated therefrom by a subsequent distillation.) This bottoms stream is removed by way of line 91.

TESTS The tests were carried out on an acid phase containing 10 moles of HF per mole of aromatic hydrocarbon and 1.5 moles of BFs per mole of aromatic hydrocarbon. The aromatic hydrocarbons contained in the acid phase were benzene, ethylxylene and xylene with some slight amounts of toluene and mesitylene. The acid phase had been prepared by treating a mixture of ethylbenzene and charged to the'column at a point 38 inches above the pot.

asoaese The column was operated at such a rate that the reflux ratio was about 0.2.

The composition of the hydrocarbons in the acid phase for each test were determined by water displacement utilizing ice cooled to acetone-Dry Ice temperature. The hydrocarbons recovered were carefully fractionated into close boiling fractions. The composition of each fraction was determined by a combination of physical properties and infrared spectrometry. The composition of the distillatively recovered ethylxylene fraction and xylene fraction was determined by infrared spectrometry. The results of the tests are set out in the table.

In Test No. B, the column was operated at a pressure of 22 p. s. i. a. using a tower top temperature of 70 F. and a bottom, i. e., column pot, temperature of 310 F. This 310 F. temperature corresponds closely to the calculated bubble point temperature for meta-xylene under these conditions. The feed rate to the column was 0.5 gallon per hour. In this test, 83% of the hydrocarbon oil charged to the column was recovered as a liquid bottoms product. The hydrocarbons taken overhead consisted of benzene and represented about 75 volume percent of the benzene present in the acid phase charged. The data show that the 1,3,5-ethylxylene present in the acid phase charged was practically, within experimental error, recovered in its entirety. However, some real back isomerization of the meta-xylene material did take place.

of the l,3,5-ethylxylene are not the same as those for the meta-xylene. The conditions may be adjusted within the ranges set out in order to maximize the purity of one material as against the other material.

Tests E and F were carried out at 78 p. s. i. a. anda reflux temperature of 95 F. These tests show that at this higher pressure, even by adjusting the temperature to the bubble point, it is not possible to operate without very considerable loss of 1,3,5-ethylxylene and prohibitive loss of meta-Xylene. It is also apparent that here the pressures are too high in that the amount of HF in the liquid bottoms product is very much higher than that obtainable in Tests B, C and D.

Thus having described the invention, what is claimed is:

1. In the process for preparing 1,3,5-ethylxylene and rn-xylene by interacting, under substantially anhydrous conditions, a feed consisting essentially of ethylbenzene and at least one xylene isomer other than m-xylene in a molar ratio of xylene to ethylbenzene of at least one in the presence of sutficient liquid HF to form a distinct separate acid phase and at least about one mole of BFa per mole of Xylene in said feed, at a temperature between about 100 F. and about 300 F. for a time between about 10 minutes and 6 hours, the longer times corresponding to the lower temperatures and recovering a hydrocarbon product from said acid phase, the improvement which comprises adding said acid phase to a continuous fractional distillation tower operating at a tower top pres- Table Test No A B O D E F Column. p. s. i. a 22 22 40 78 78 Column Pot, F 250 310 312 321 334 372 Column Charge, Mole Percent:

1,3,5 In Ethylxylene Portion 97. 9 97.9 99. 5 99. 6 99 99 metain Xylene Portion 96.8 96.4 96. 7 96 96 Column Product, Mole Percent:

1.3.5- in Ethylxylone Portion 96. 4 97. 5 97. 2 98. 6 93 94 metain Xylene Portion 96.1 93. 5 93.3 83 83 Cltrange in Purity by Back-isomerizalon:

1,3,5-Ethylxylene 1. 5 0. 4 2. 3 -1. 0 --6 -5 m-Xylene -0. 7 -2. 9 3. 4 13 13 HF in Aromatic Pot Product, Wt.

Percent 0. 18 0. 07 0. 07 0. 06 0. 20 0. 14 BF; in Aromatic Pet Product, p. p. m. 2. 4 2. 5

Test No. A was carried out under about the same conditions as Test B except that the pot temperature was deliberately made 250 F. or very much lower than the calculated bubble point of meta-xylene. The results show that a very appreciable amount of 1,3,5-ethylxylene was isomerized to other ethylxylenes. Furthermore, the acid content of the liquid hydrocarbon product from the pot in Test A was almost triple that of the pot product in Test B.

Tests C and D were carried out at the same column pressure of 40 p. s. i. a. and at temperatures only 9 degrees apart, Test D being carried out at about the bubble point of meta-xylene at these conditions. The results of the tests show that Test No. D produced quite a bit less back isomerization of the 1,3,5-ethylxylene but produced somewhat more back isomerization of the meta-xylene. These tests show that optimum conditions for highest purity sure between about 20 and 60 p. s. i. a. and a tower pot temperature of essentially the bubble point of m-xylene at the particular pressure, removing overhead from the tower HF, BF3 and hydrocarbons and removing a bottom product ethylxylene and Xylene of essentially the same purity as existed in said acid phase.

2. The process of claim 1 wherein the tower pot" temperature is between about 305 F. and 345 F., the lower temperatures corresponding to the lower pressures.

3. The process of claim 1 wherein the tower pot temperature is about 320 F. and the tower top pressure is about 40 p. s. i. a.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN THE PROCESS FOR PREPARING 1,3,5-ETHYLXYLENE AND M-XYLENE BY INTERACTING, UNDER SUBSTANTIALLY ANHYDROUS CONDITIONS, A FEED CONSISTING ESSENTIALLY OF ETHYLBENZENE AND AT LEAST ONE XYLENE ISOMER OTHER THAN M-XYLENE IN A MOLAR RATIO OF XYLENE TO ETHYLBENZENE OF AT LEAST ONE IN THE PRESENCE OF SUFFICIENT LIQUID HF TO FORM A DISTINCT SEPARATE ACID PHASE AND AT LEAST ABOUT ONE MOLE OF BF3 PER MOLKE OF XYLENE IN SAID FEED, AT A TEMPERATURE BETWEEN ABOUT 100*F. AND ABOUT 300*F. FOR A TIME BETWEEN ABOUT 10 MINUTES AND 6 HOURS, THE LONGER TIMES CORRESPONDING TO THE LOWER TEMPERATURES AND RECOVERING A HYDROCARBON PRODUCT FROM SAID ACID PHASE, THE IMPROVEMENT WHICH COMPRISES ADDING SAID ACID PHASE TO A CONTINUOUS FRACTIONAL DISTILLATION TOWER OPERATING AT A "TOWER TOP" PRESSURE BETWEEN ABOUT 20 AND 60 P.S.I.A.AND A "TOWER POT" TEMPERATURE OF ESSENTIALLY THE BUBBLE POINT OF M-XYLENE AT THE PARTICULAR PRESSURE, REMOVING OVERHEAD FROM THE TOWER HF, BF, AND HYDROCARBONS AND REMOVING A BOTTOM PRODUCT ETHYLXYLENE AND XYLENE OF ESSENTIALLY THE SAME PURITY AS EXISTED IN SAID ACID PHASE. 